Long burning delay blasting caps

ABSTRACT

Delay type blasting caps in which the burning time of the delay fuse is at least 1.5 seconds per inch with accompanying low sensitivity to ignition, which, due to novel ignition system structure, provide for elimination of premature venting of heat and pressure required for ignition of the delay fuse and concomitant failure of the shot. The delay blasting caps include explosive base charge, primer, and delay charges in that order, and an ignition assembly above the delay charge, with or without an intermediately disposed wafer charge. The ignition assembly is a tube containing the ignition charge, as a core, having a heat of reaction of at least 50 calories per gram. When the wafer charge is included, the heat of reaction of the ignition charge is generally from 50 to about 100 calories per gram, and the heat of reaction of the wafer charge is from about 60 to 105 calories per gram; and when the ignition charge is the sole source of heat for ignition of the delay, its heat of reaction is higher, generally up to about 150 calories per gram, but higher in some embodiments, sometimes as high as about 600 calories per gram.

ilited States Patent [191 Zebree Primary Examiner-Verlin R. Pendegrass Attorney, Agent, or Firm-S. Grant Stewart July 22, 1975 5 7 ABSTRACT Delay type blasting caps in which the burning time of the delay fuse is at least 1.5 seconds per inch with accompanying low sensitivity to ignition, which, due to novel ignition system structure, provide for elimination of premature venting of heat and pressure required for ignition of the delay fuse and concomitant failure of the shot.

The delay blasting caps include explosive base charge, primer, and delay charges in that order, and an ignition assembly above the delay charge, with or without an intermediately disposed wafer charge. The ignition assembly is a tube containing the ignition charge, as a core, having a heat of reaction of at least calories per gram. When the wafer charge is included, the heat of reaction of the ignition charge is generally from 50- to about calories per gram, and the heat of reaction of the wafer charge is from about 60 to calories per gram; and when the ignition charge is the sole source of heat for ignition of the delay, its heat of reaction is higher, generally up to about 150 calories per gram, but higher in some embodiments, sometimes as high as about 600 calories per gram.

7 Claims, 4 Drawing Figures LONG BURNING DELAY BLASTING CAPS This invention relates to long burning time delay type blasting caps. In one aspect this invention relates to delay type blasting caps in which the delay fuse has a burning time of at least 1.5 seconds per inch and thereby has a relatively low sensitivity to ignition, and to an ignition system therein imparting the requisite heat for reliably igniting the delay fuse. Other aspects will be apparent in light of the accompanying disclosure and the appended claims.

Delay type blasting caps comprise a closed shell loaded with base charge, primer, delay fuse and ignition components in that order for initiation by suitable initiator means. The delay charge, or fuse, intermediate the ignition and primer charges, is disposed to burn over a predetermined time duration in response to ignition of the ignition charge, and hence to delay communication of the ignition with the primer until expiration of the delay fuse burning time.

Long burning delay charges are characterized by a corresponding decrease in sensitivity to ignition, often requiring a supplemental hot, i.e., high temperature burning, wafer, or booster, type charge intermediate the ignition and delay charge; the wafer, ignitable in response to action of the ignition charge thus supplementing the latter to impart the necessary high heat requirements for ignition of the delay fuse.

Often, due to the heat and pressure buildup in the delay ignition area, a premature venting of heat and pressure required for ignition of the delay fuse takes place with concomitant failure of the shot. The venting proceeds along a path above the ignition charge through a cap portion initially encompassing the blasting cap initiator means.

In the initiation of long delay period blasting caps by action of a detonator cord, the force of detonation of the emplaced detonator cord causes rupture of the adacent shell portion to, in turn, cause heat and pressure developed in the ignition area to vent from the thus ruptured shell to the atmosphere prior to ignition of the delay fuse, often with accompanying failure of the shot.

it has thus been necessary in those instances, in order to assure a successful delay fuse ignition, that the ignition system be sufficiently high temperature burning, and present in amount, to provide heat and pressure in excess of that actually required for igniting the delay fuse to compensate for that lost from the ruptured shell. However, inasmuch as the extent of actual venting of heat and pressure is always uncertain, the amount vented in any instance is often excessive in which event there is insufficient residual heat and pressure within the ignition area for ignition of the delay fuse; or, the vented amount is too small in which event the unduly large amount of heat and pressure in the ignition area causes premature rupture of its surrounding shell portion with accompanying failure of the delay fuse ignition.

1n the use of a black powder, or similar core type initiator for long burning delay caps, the unfilled portion of the cord after burning of the black powder is often unobstructed sufficiently to constitute a passageway for the premature venting of pressure and heat from the ignition area.

1n the electrical initiation of long burning delay caps, the heat and pressure developed in the ignition area has caused the ignition plug to be blown from the shell with the premature venting of pressure and heat from the cap along a path vacated by the plug.

In my eopending application Ser. 267,327 filed June 29, 1972, now US. Pat. No. 3,776,135 hereinafter referred to as my copending application Ser. No. 267,327, I have disclosed delay type detonator cordinitiated blasting cap assemblies which include an open cavity immediately above and adjacent the ignition system and partially closed at its upper end by constriction means, for receiving such excess heat and pressure from the ignition area; the cavity volume being correlated with the cross sectional area of the constriction to permit heat and pressure not required for the ignition to vent through the cavity and constriction to the atmosphere through the shell portion ruptured by detonation of the cord, but to cause sufficient heat and pressure to be retained in the ignition area for ignition of the delay fuse.

This invention is concerned with long burning delay period caps including an ignition assembly providing for elimination of the above described premature venting of heat and pressure from the ignition system to thereby retain sufficient heat and pressure in the delay ignition area for the necessary delay period and subsequent detonation.

In accordance with the invention, a long burning delay blasting cap assembly is provided which comprises,

a closed shell including a plug member in one end as a closure member therefor;

an explosive base charge, a primer charge and a delay charge in said shell, extending in that order toward said plug closure, and said delay charge having a burning time of at least 1.5 seconds per inch;

an ignition assembly in said shell extending from said plug closure into superposed relationship with said delay charge, including a tube member transversely closing said shell and an ignition charge having a heat of reaction of at least 50 calories per gram within said tube member as a core therein, and said core charge disposed in operative ignition relationship with said delay charge, with or without an intermediately disposed ignition booster charge as a supplemental source of heat for ignition of said delay charge; and

means in said plug closure for support of initiator means for said cored ignition charge.

In preferred practice, an ignition booster, or wafer, charge is disposed intermediate the cored ignition and the delay charge, but, contrary to that in the assembly disclosed in my copending application Ser. No. 267,327, it has a heat of reaction less than about 110 calories per gram, and more often in the range of from about 60 to 105 calories per gram; and in that embodiment the heat of reaction of the core ignition charge is generally within the range of from about to calories per gram.

The invention is further illustrated with reference to the drawings of which FIG. 1 is a delay blasting cap assembly of the invention in which the delay fuse is a core type charge compacted in a metal tube;

FIG. 2 illustrates an embodiment the same as that of FIG. 1 except that the delay fuse is a consolidated charge;

FIG. 3 is the same as FIG. ll except that a wafer, or booster, type ignition charge is disposed between the ignition and delay assemblies to facilitate ignition of the delay fuse; and

FIG. 4 illustrates the embodiments of FIGS. 1, 2 and 3, each including a low energy detonator cord supported in initiating relationship with the ignition system. All like parts shown in the drawings are designated by like numbers.

Referring to FIG. 1, elongated shell contains base charge 11 adjacent integrally closed shell end 12, primer charge assembly 13 superposed on charge 11, delay charge assembly 14 superposed on assembly 13, ignition charge assembly 16 superposed on assembly 14 and ignition type closure plug 17 at the opposite end 12 containing passageway 18 extending longitudinally therethrough for support of a detonator cord in initiating relationship with ignition assembly 16. Ignition plug 17 is supported in shell 10 by any suitable means such as by interference fit, staking, or by one or more peripheral crimps 20 (see FIG. 4) along the outer periphery of shell 10.

Ignition assembly 16 includes any suitable shock, or heat, sensitive ignition charge 16a as a core member compacted in lead tube 16b, the latter substantially closing shell 10. Core charge 16a is of sufficient sensitivity to be directly responsive to ignition by a low energy detonator cord supported in passageway 18; and, in the embodiment shown, charge 16a has a sufficiently high heat of reaction for a direct transfer to delay charge 14a for ignition of the latter.

Exemplary core ignition charges utilized in practice of the invention include lead/selenium, leadtin/selenium, tin/selenium, red lead/boron, lead oxide (PbO)/boron, and red lead/manganese boride.

Any suitable form of delay assembly can be utilized in lieu of now preferred delay assembly 14, which is of the core type including delay fuse 14a compacted in lead tube 14b, the latter in substantially closed relationship with shell 10. Delay fuse 14a of the longer burning type, and hence of correspondingly decreased sensitivity to ignition, has a burning time of at least 1.5 seconds per inch, generally within the range of from about 2-12 seconds per inch. Barium peroxide/selenium, barium peroxide/tellurium and barium peroxide/tellurium/- selenium in the requisite proportions provide for the above described burning times, and are further exemplary of delay fuse compositions utilized in the practice of the invention.

Exemplary primer charges that can be utilized in the practice of the invention include diazodinitrophenol, nitromanite and the like. Now preferred is a diazodinitrophenol system 13 including a metal capsule 13a open at each end and extending substantially coaxially within, and in closing relationship with, shell 10; a diazodinitrophenol Wafer charge 13b pressed above, and on, capsule 13a and of sufficiently high density to be ignitable in response to combustion of the delay charge 14a; and diazodinitrophenol charge 130 within capsule 13a of sufficiently low density to be detonat able in response to heat developed by ignition of charge 13b to, in turn, cause detonation of base charge 11.

Exemplary base explosive charges that can be utilized in the delay caps of the invention include such as pentaerythritol tetranitrate, cyclonite (RDX), trinitrophenylmethylnitramine, and the like.

Although the ignition system of the delay cap assemblies of the invention is always of the core type illustrated with reference to FIG. 1, the longer burning delay charge is not limited to the core type of FIG. 1 but can be a consolidated charge such as delay charge 14 of FIG. 2. The assembly of FIG. 2 is, in all other aspects, the same as that of FIG. 1.

With reference to FIG. 4 is shown an assembly of FIGS. 1, 2 or 3 including closure ignition plug 17 within top end 12' and including low energy detonator cord 22 extending from outside shell 10 into passageway 18 and into initiating relationship with the cored ignition charge supported in tube 16b. As shown, the detonator cord 22 is substantially in direct contact initiating relationship with the cored ignition charge. However, detonator cord 22 can terminate in position spaced from the cored charge so long as it remains in initiating relationship therewith. Ignition plug member 17 can be formed from any suitable material such as a suitable plastic, cork, rubber, lead and the like. Any suitable core loading of detonator cord 22 can be utilized, generally a loading of from about 2 to 6 grains PETN (or equivalent) per linear foot is preferred. Initiation of detonator cord 22 outside the cap assembly can be accomplished in any suitable manner such as in response to detonation of an electrical blasting cap, or in association with a trunk type detonator cord of heavier loadings, say in the order of about 25 grains PETN per linear foot.

The invention is further illustrated with reference to several series of tests summarized as follows:

A first set of delay blasting caps having the configuration of FIG. 3 of the drawings was made up and initiated utilizing a low energy detonator cord initiator having an outside diameter of 0.104 inches i 0.004 inches, and a core loading of 3-6 grains PETN per linear foot, emplaced as illustrated with reference to FIG. 4. Each delay cap, with reference to FIG. 3, was formed from a shell 10 having a length of 3.12 inches and an inside diameter of 0.256 inches, and contained:

Base charge 11 PETN, 0.40 gram Primer Assembly 13 Capsule 13a Diazodinitrophenol Charge 13b, 0.06 gram Density about 1.6 grams/cc Charge 13c, 0.24 gram Density about 1.10 grams/cc Delay Assembly 14" Lead tube 14b Outside diameter, 0.25 inch Length, 1.00 inch Perforation diameter, 0.1 l0 inch Delay charge 14a BaO /Te/Se (40/40/20) (about 1.0 gram) Ignition Booster Charge 19 (see tabulation) Test Series No. l, 0.20 gram Test Series No. 2, 0.20 gram Test Series No. 3, 0.20 gram Ignition Assembly 16 Lead Tube 16b Length, 1.0 inch Outside Diameter, 0.252 inch Perforation diameter, 0.1 10 inch Ignition Charge 16a PbSn/Se (72/28) about 2.5 grams Closure Plug 17,

Polyethylene, about 1.0 inch Passageway 18,

Length, about 1.0 inch There were no failures of the tests of Series 3, the heat of reaction in charge 19 in this series being lower than that of the Series 1 and 2, viz. 70 calories per gram. The tests of Series 3 demonstrate successful igni- Diameter, about 0.120 inch 5 tion of the delay fuse, when utilizing an intermediate A second set of delay blasting caps having the same ignition booster, or wafer charge having a heat of reacconfiguration, and charge components in the same tion within the range of 60-105 calories per gram. amounts, as those of FIG. 3 above described were made up and tested except that the passageway 18 The Series 4 tests demonstrate satisfactory results obin the ignition plug was divided by a constriction l0 tamed in the absence of an lgmtion booster charge, alimo a resulting lower passageway, and the passage though there were three failures of the ten tests of the way 18 being further Closed by a wb member FIG. 3 configuration and three of the five tests of the stantially immediately above the constriction, the mPdIfied configinatlon these fallures g latter functioning to intercept and stop ingress of tflbutable 9 fnsufficlency of h gnefated by the detonator cord and to protect the cap interior tion of the ignition charge to reliably ignite the solafrom moisture ingress during storage. Each delay Cgm delay ,fuse; and hence F need for an m?" cap of this second set was that of the configuration Charge? havmg a Somewhat higher heat of reacnon m of delay blasting caps containing cavity and the those Instances constriction Stfucture abQVe dFScribed with f The examples further demonstrate the function of ence'to F 6 m the Speclficatlon of my copendmg 20 the cored ignition charge structure with reference to aPPhcanon N 267,327- the unexpected low heat of reaction of the wafer or each of three Senes of tests delay blasnflg Caps of booster charge that is required. It appears that this sureach of first Second Sets abow descnbed, were prisingly low heat of reaction requirement is the result tested for initiatability. The blasting caps tested were of function of the cored ignition harge to balance un- Same throughout three Series except that expectedly small amounts of heat and pressure vented Ihollgh the Wafer or igmtion booster, charge 19 from the ignition area with that retained for ignition of position was the same throughout each series, it was the relatively insensitive delay f varied for each of the other series.

In a fourth series of tests, delay blasting caps, the Now preferred, and further illustrative of core type same as those of the first three series, were similarly ignition charges utilized as the sole source of heat for tested except that they were devoid of a wafer charge. ignition of the delay fuse, as shown in FIG. 1, are The results of the tests are tabulated as follows. *Pb O -MnB 90-10, and Pb O -B, 94-6; and simi- Table Wafer Charge 19 Configuration Test Resp. Component Heat of 1st Set** 2nd Set*** ISenes Components Weight Rates Reaction* Tested Failed Tested Failed 1 Fe O /Al/B/PbSn/Se/ 15.0/ I 2.0/2.5/48.6/ 400 5 3 5 4 Snow Floss 189/30 1 Fe O /Al/B/PbSn/Se/ 3.75/3.00/().625/64.53/ 172 5 1 5 0 Snow Floss 25.095/3.00 3 PbSn/Se 72/28 70 10 0 l0 0 4 None i0 3 5 3 "Calories per gram Configuration of FIG 3 '"Configurution of FIG. 3 modified to include constriction and web closure of the copcnding 327 application.

In the tests of Series 1, three of the five caps of the configurations of FIG. 3 (1st set) and four of the five of the modified FIG. 3 configuration (2nd set) were failures, due to excessive heat and pressure generated by the booster charge 19, thus causing the blasting cap shell to burst adjacent to ignition area with loss, by venting, of the heat and pressure for ignition of the delay fuse; thus demonstrating the need for correlation of choice of the ignition and wafer charges for the balance of heat and pressure required.

In the five tests of Series 2 there was only one failure of the FIG. 3 configuration and there were no failures larly, now preferred core ignition charges utilized in combination with an ignition booster, or wafer charge, as illustrated with reference to FIG. 3, are (weight basis) PbSn-Se, 72-28, PbO-B, 88-12, Pb O -MnB 85-15, and Pb O -B, -20. weight basis) What I claim and desire to protect by Letters Patent 1. A long burning delay blasting cap assembly which comprises,

a closed shell, including a plug closure member therefor; an explosive base charge, a primer charge and a delay charge disposed in said shell in that order toward said plug closure, said base charge detonatable in response to detonation of said primer charge and said primer charge detonatable in response to burning of said delay charge, and said delay charge having a burning time of at least 1.5 seconds;

an ignition assembly in said shell intermediate said plug closure and said delay charge, including a tube member and an ignition charge within said tube member as a core therein, and said core ignition charge having a heat of reaction of at least 50 calories per gram;

a booster ignition charge having a heat of reaction of 5 at least 60, but less than about 110, calories per gram intermediate said core ignition and delay charges, said booster ignition charge being ignitable in response to burning of said core ignition charge, and said delay charge being ignitable by heat and pressure from burning of said core and booster ignition charges; and

means in said plug closure for support of initiator means for said core ignition charge 2. A blasting cap assembly of claim 1 wherein said booster ignition charge has a heat of reaction of from about 60 to 105 calories per gram, and said core ignition charge has a heat of reaction of from about 70 to 100 calories per gram.

3. A blasting cap assembly of claim 2 wherein the burning time of said delay charge is from about 2 to 12 seconds per inch.

4. A blasting cap assembly of claim 3 wherein said shell is elongated and said plug closure is an end closure member therefor. said plug closure contains a passageway longitudinally extending therethrough in communication with the outside of said shell and with the interior thereof, for support of said initiator means, said tube member transversely closes said shell and extends longitudinally from said closure plug and is superposed on said booster ignition charge, and said booster ignition charge is superposed on said delay charge.

5. A blasting cap assembly of claim 4 wherein said delay charge is consolidated in said shell.

6. A blasting cap assembly of claim 4 wherein said delay charge forms a core of a metal tube transversely closing, and longitudinally extending in, said shell.

7. In a blasting cap assembly of claim 4, a detonator cord having a core loading of from 2 to 6 grains PETN (or equivalent) per foot supported in said passageway as said initiator means. 

1. A long burning delay blasting cap assembly which comprises, a closed shell, including a plug closure member therefor; an explosive base charge, a primer charge and a delay charge disposed in said shell in that order toward said plug closure, said base charge detonatable in response to detonation of said primer charge and said primer charge detonatable in response to burning of said delay charge, and said delay charge having a burning time of at least 1.5 seconds; an ignition assembly in said shell intermediate said plug closure and said delay charge, including a tube member and an ignition charge within said tube member as a core therein, and said core ignition charge having a heat of reaction of at least 50 calories per gram; a booster ignition charge having a heat of reaction of at least 60, but less than about 110, calories per gram intermediate said core ignition and delay charges, said booster ignition charge being ignitable in response to burning of said core ignition charge, and said delay charge being ignitable by heat and pressure from burning of said core and booster ignition charges; and means in said plug closure for support of initiator means for said core ignition charge.
 2. A blasting cap assembly of claim 1 wherein said booster ignition charge has a heat of reaction of from about 60 to 105 calories per gram, and said core ignition charge has a heat of reaction of from about 70 to 100 calories per gram.
 3. A blasting cap assembly of claim 2 wherein the burning time of said delay charge is from about 2 to 12 seconds per inch.
 4. A blasting cap assembly of claim 3 wherein said shell is elongated and said plug closure is an end closure member therefor, said plug closure contains a passageway longitudinally extending therethrough in communication with the outside of said shell and with the interior thereof, for support of said initiator means, said tube member transversely closes said shell and extends longitudinally from said closure plug and is superposed on said booster ignition charge, and said booster ignition charge is superposed on said delay charge.
 5. A blasting cap assembly of claim 4 wherein said delay charge is consolidated in said shell.
 6. A blasting cap assembly of claim 4 wherein said delay charge forms a core of a metal tube transversely closing, and longitudinally extending in, said shell.
 7. In a blasting cap assembly of claim 4, a detonator cord having a core loading of from 2 to 6 grains PETN (or equivalent) per foot supported in said passageway as said initiator means. 